(1) Field of the Invention
The present invention relates to a system and method for automatically controlling cruising speed of a vehicle having a learning function to optimize operation control parameters during a period of running control operation of the vehicle using the system.
(2) Background Art
Automatic cruising speed controlling apparatus (so called, Auto Speed Control Device: ASCD) are mounted on vehicles in which, when a desired cruising speed is set during the ASCD operation, the vehicle can run at the desired cruising speed without operation of the accelerator pedal of the vehicle.
One of such automatic cruising speed controlling apparatus will be described below.
When a main switch of the cruising speed controlling apparatus is turned to ON, a contact of an ASCD relay is closed to transmit a power supply voltage to a controller.
When any one of set switch, resume (reset) switch, and an accelerate switch is operated in a given state, the controller receives a signal indicative of a vehicle speed from a vehicle speed sensor. Then, the controller sets, modifies, and stores a target vehicle speed. When the vacuum valve, ventilation valve, and/or safety release valve of a throttle actuator is appropriately actuated, the opening angle of the throttle valve of the vehicular engine is controlled by means of a diaphragm actuator. The diaphragm actuator includes the vacuum valve, ventilation valve, and release valve.
In addition, the controller outputs a signal to an A/T (Automatic transmission) controller to control gear selection of the transmission so that the vehicle speed remains constant even when load on the vehicle varies.
When the ASCD is operated to cruise the vehicle at the desired cruising speed, control parameters K.sub.1 and K.sub.2 are previously determined. An operation variable u of the throttle valve opening angle is determined from such a control arithmetic operation equation as u=K.sub.1 e+K.sub.2 .DELTA.e. In the equation, e denotes control deviation, i.e., the difference between the target vehicle speed v.sub.s and current vehicle speed v (e=v.sub.s &lt;v) derived from the vehicle speed sensor and .DELTA.e denotes one step difference (.DELTA.e=e'-e) between the current vehicle speed e and the previous vehicle speed e' one control period before.
When the ASCD operation is cancelled, the vehicle speed value at the time of cancelling the ASCD operation is stored as a stored vehicle speed. Thereafter, when the resume switch is operated, the vehicle speed is returned to the stored vehicle speed.
However, since control constants, i.e., the control parameters K.sub.1 and K.sub.2 in the equation u=K.sub.1 e+K.sub.2 .DELTA.e are varied according to a model of the vehicle using the system, a certain time is required to determine the values of the control parameters K.sub.1 and K.sub.2.
To avoid having to make the determinations of the control parameters, another automatic cruising speed controlling apparatus has been proposed in which a learning function is provided as a part of determining constants, e.g., control parameters to achieve a self calibrating operation.
In detail, the automatic cruising speed controlling apparatus detects the current vehicle speed value v derived from the vehicle speed sensor. The controller installed in the system calculates the control deviation e and one step difference .DELTA.e from the current vehicle speed v and target vehicle speed v.sub.s and substitutes the calculated control variation e and one step difference .DELTA.e into the control arithmetic operation equation u=K.sub.1 e+K.sub.2 .DELTA.e. In this way, the operating variable u of the opening angle of the throttle valve is determined so that the vehicle speed approaches the target value.
In the above-described controller, only the above-described control operation is repeated when an evaluation start section thereof is commerced in the control operation mode of, e.g., a resume operation to return the vehicle speed to the original set vehicle speed. On the other hand, the evaluation operation goes to a learning operation mode and the learning of the control parameters K.sub.1 and K.sub.2 is carried out to optimize the control parameters K.sub.1 and K.sub.2.
That is to say, the control parameters K.sub.1 and K.sub.2 which do not generate large errors in normal states are previously set irrespective of vehicle operation characteristics. When the vehicle runs at the cruising speed with the above-described ASCD system operated, an overshooting or undershooting of control frequently occurs due to inappropriate setting of the control parameters for the individual vehicle using the system.
Therefore, control characteristics of the system during a given control period are evaluated by means of an evaluation part in the controller when the evaluation start section is operated. To achieve more appropriate control characteristics, the control parameters K.sub.1 and K.sub.2 are reviewed and updated on the basis of the evaluation results in a control parameter change operation section thereof.
In addition, when the above-described control procedure is again started, the control characteristics are evaluated and reviewed and the control parameters K.sub.1 and K.sub.2 are updated according to the evaluation results so as to produce optimum control parameters.
However, the evaluation and review for the vehicle speed control characteristics are difficult due to difficulty in obtaining most appropriate control characteristics in the previously proposed automatic cruising speed controlling system. In addition, when the control characteristics to be evaluated peculiarly respond due to an occasional generation of disturbance, the automatic cruising speed controlling system cannot detect the peculiarly responded control characteristics. Therefore, the system evaluates and learns the control parameters to follow the peculiar response. Consequently, the control characteristics in response to normal operating conditions becomes worsened and hunting of the vehicle speed occurs with or without disturbance.